Check out example codes for "form css". It will help you in understanding the concepts better.

Code Example 1

border: none;
border-bottom: 1px solid blue;

Code Example 2

<!DOCTYPE html>
<html>
<style>
input[type=text], select {
  width: 100%;
  padding: 12px 20px;
  margin: 8px 0;
  display: inline-block;
  border: 1px solid #ccc;
  border-radius: 4px;
  box-sizing: border-box;
}

input[type=submit] {
  width: 100%;
  background-color: #4CAF50;
  color: white;
  padding: 14px 20px;
  margin: 8px 0;
  border: none;
  border-radius: 4px;
  cursor: pointer;
}

input[type=submit]:hover {
  background-color: #45a049;
}

div {
  border-radius: 5px;
  background-color: #f2f2f2;
  padding: 20px;
}
</style>
<body>

<h3>Using CSS to style an HTML Form</h3>

<div>
  <form action="/action_page.php">
    <label for="fname">First Name</label>
    <input type="text" id="fname" name="firstname" placeholder="Your name..">

    <label for="lname">Last Name</label>
    <input type="text" id="lname" name="lastname" placeholder="Your last name..">

    <label for="country">Country</label>
    <select id="country" name="country">
      <option value="australia">Australia</option>
      <option value="canada">Canada</option>
      <option value="usa">USA</option>
    </select>
  
    <input type="submit" value="Submit">
  </form>
</div>

</body>
</html>

Code Example 3

/* Answer to: "css form styling" */

/*
  Style your forms just like you would do for any other element!
  I found an example given by W3Schools (link in the source).
*/

* {
  box-sizing: border-box;
}

input[type=text], select, textarea {
  width: 100%;
  padding: 12px;
  border: 1px solid #ccc;
  border-radius: 4px;
  resize: vertical;
}

label {
  padding: 12px 12px 12px 0;
  display: inline-block;
}

input[type=submit] {
  background-color: #4CAF50;
  color: white;
  padding: 12px 20px;
  border: none;
  border-radius: 4px;
  cursor: pointer;
  float: right;
}

input[type=submit]:hover {
  background-color: #45a049;
}

.container {
  border-radius: 5px;
  background-color: #f2f2f2;
  padding: 20px;
}

.col-25 {
  float: left;
  width: 25%;
  margin-top: 6px;
}

.col-75 {
  float: left;
  width: 75%;
  margin-top: 6px;
}

/* Clear floats after the columns */
.row:after {
  content: "";
  display: table;
  clear: both;
}

/* Responsive layout - when the screen is less than 600px wide, make the two columns stack on top of each other instead of next to each other */
@media screen and (max-width: 600px) {
  .col-25, .col-75, input[type=submit] {
    width: 100%;
    margin-top: 0;
  }
}
/*
  HTML:
  <!DOCTYPE html>
  <html>
  <head>
  <meta name="viewport" content="width=device-width, initial-scale=1">

  </head>
  <body>

  <h2>Responsive Form</h2>
  <p>Resize the browser window to see the effect. When the screen is less than 600px wide, make the two columns stack on top of each other instead of next to each other.</p>

  <div class="container">
    <form action="/action_page.php">
      <div class="row">
        <div class="col-25">
          <label for="fname">First Name</label>
        </div>
        <div class="col-75">
          <input type="text" id="fname" name="firstname" placeholder="Your name..">
        </div>
      </div>
      <div class="row">
        <div class="col-25">
          <label for="lname">Last Name</label>
        </div>
        <div class="col-75">
          <input type="text" id="lname" name="lastname" placeholder="Your last name..">
        </div>
      </div>
      <div class="row">
        <div class="col-25">
          <label for="country">Country</label>
        </div>
        <div class="col-75">
          <select id="country" name="country">
            <option value="australia">Australia</option>
            <option value="canada">Canada</option>
            <option value="usa">USA</option>
          </select>
        </div>
      </div>
      <div class="row">
        <div class="col-25">
          <label for="subject">Subject</label>
        </div>
        <div class="col-75">
          <textarea id="subject" name="subject" placeholder="Write something.." style="height:200px">

Code Example 4

table, th, td {
    padding: 1.5%;
    border: 1px solid white;
    text-align: center;
}

button{
    width: 100%;
    height: 100%;
    padding: 2px ;
    margin: 2px;
}

body {
    background-image: url(https://images.unsplash.com/photo-1574375927938-d5a98e8ffe85?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=1949&q=80);
    height: 100%;
    
    background-position: center;
    background-repeat: no-repeat;
    background-size: cover;
    color: honeydew;
}

.h1-header, h1{
    text-align: center;
    width: 100%;
    height: 70px;
    font-size: 14px;
    padding-top:0px ;
}
h1 {
    font-size: 36px;
    font-style: italic;

}
.form1 {
    float: left;

width: 20%;
height: 300px;
margin: 150px 0 0 200px;
    background-color: #3a303099;

}
.form1 #form {
    color: honeydew;
    
}
form{
    padding: 50px;
    }
    

.table {
    width: 35%;
    margin: 150px 200px 0 800px;

}

table{
padding: 50px 120px;
}

Code Example 5

{
  box-sizing: border-box;
}

input[type=text], select, textarea {
  width: 100%;
  padding: 12px;
  border: 1px solid #ccc;
  border-radius: 4px;
  resize: vertical;
}

label {
  padding: 12px 12px 12px 0;
  display: inline-block;
}

input[type=submit] {
  background-color: #4CAF50;
  color: white;
  padding: 12px 20px;
  border: none;
  border-radius: 4px;
  cursor: pointer;
  float: right;
}

input[type=submit]:hover {
  background-color: #45a049;
}

.container {
  border-radius: 5px;
  background-color: #f2f2f2;
  padding: 20px;
}

.col-25 {
  float: left;
  width: 25%;
  margin-top: 6px;
}

.col-75 {
  float: left;
  width: 75%;
  margin-top: 6px;
}

/* Clear floats after the columns */
.row:after {
  content: "";
  display: table;
  clear: both;
}

/* Responsive layout - when the screen is less than 600px wide, make the two columns stack on top of each other instead of next to each other */
@media screen and (max-width: 600px) {
  .col-25, .col-75, input[type=submit] {
    width: 100%;
    margin-top: 0;
  }
}
/*
  HTML:
  <!DOCTYPE html>
  <html>
  <head>
  <meta name="viewport" content="width=device-width, initial-scale=1">

  </head>
  <body>

  <h2>Responsive Form</h2>
  <p>Resize the browser window to see the effect. When the screen is less than 600px wide, make the two columns stack on top of each other instead of next to each other.</p>

  <div class="container">
    <form action="/action_page.php">
      <div class="row">
        <div class="col-25">
          <label for="fname">First Name</label>
        </div>
        <div class="col-75">
          <input type="text" id="fname" name="firstname" placeholder="Your name..">
        </div>
      </div>
      <div class="row">
        <div class="col-25">
          <label for="lname">Last Name</label>
        </div>
        <div class="col-75">
          <input type="text" id="lname" name="lastname" placeholder="Your last name..">
        </div>
      </div>
      <div class="row">
        <div class="col-25">
          <label for="country">Country</label>
        </div>
        <div class="col-75">
          <select id="country" name="country">
            <option value="australia">Australia</option>
            <option value="canada">Canada</option>
            <option value="usa">USA</option>
          </select>
        </div>
      </div>
      <div class="row">
        <div class="col-25">
          <label for="subject">Subject</label>
        </div>
        <div class="col-75">
          <textarea id="subject" name="subject" placeholder="Write something.." style="height:200px">

Code Example 6

#form {

    border: 1px solid black;
    padding: 1.5%;
    text-align: center;
    

}

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