Bootstrap 4 

<!doctype html>
<html lang="en"> <head> <!-- Required meta tags --> <meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<title>Bootstrap 4</title>
html { -webkit-box-sizing: border-box; -moz-box-sizing: border-box; box-sizing: border-box; }
*, *:before, *:after { -webkit-box-sizing: inherit; -moz-box-sizing: inherit; box-sizing: inherit; }
<link rel="stylesheet" href="" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous">
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Bootstrap 4 - Forms

Bootstrap provides several form control styles, layout options, and custom components for creating a wide variety of forms.

Bootstrap 4 - Modal

Bootstrap 4 - DropDowns

Bootstrap Select

<div class="selectWrapper">
.selectWrapper {
    width: 100%;
    overflow: hidden;
    position: relative;
    border: 1px solid #bbb;
    border-radius: 2px;
    background:#FFFFFF url('data:image/svg+xml,') right 13px center no-repeat;

    .selectWrapper select {
        padding: 12px 40px 12px 20px;
        font-size: 18px;
        line-height: 18px;
        width: 100%;
        border: none;
        box-shadow: none;
        background: transparent;
        background-image: none;
        -webkit-appearance: none;
        outline: none;
        cursor: pointer;
        -moz-appearance: none;
        text-indent: 0.01px;
        text-overflow: ellipsis;


Bootstrap-select is a jQuery plugin that utilizes Bootstrap's dropdown.js to style and bring additional functionality to standard select elements.

<!-- Latest compiled and minified CSS -->
<link rel="stylesheet" href="">

<!-- Latest compiled and minified JavaScript -->
<script src=""></script>

Bootstrap 3

<!DOCTYPE html>
        <meta name="viewport" content="width=device-width, initial-scale=1">
        <link rel="stylesheet" href="">
        <script src=""></script>
        <script src=""></script>
<div class="container">
            <p>The .dropdown class is used to indicate a dropdown menu.</p>
            <p>Use the .dropdown-menu class to actually build the dropdown menu.</p>
            <p>To open the dropdown menu, use a button or a link with a class of .dropdown-toggle and data-toggle="dropdown".</p>
            <div class="dropdown">
                <button class="btn btn-primary dropdown-toggle" type="button" data-toggle="dropdown">Dropdown Example
                <span class="caret"></span></button>
                <ul class="dropdown-menu">
                    <li><a href="#">HTML</a></li>
                    <li><a href="#">CSS</a></li>
                    <li><a href="#">JavaScript</a></li>