Design view not getting displayed on Android Studio

I just imported a project, but when i try to enter design view this shows up:

My current gradle version is the latest 26.0.2 by the way. I'm not sure what to do, anyone have an idea?

Here are some Gradle Scripts:

apply plugin: 'com.android.application'

android {
    compileSdkVersion 23
    buildToolsVersion

    defaultConfig {
        applicationId "com.example.Ron.myapp"
        minSdkVersion 15
        targetSdkVersion 23
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    testCompile 'junit:junit:4.12'
    compile 'com.android.support:appcompat-v7:23.1.1'
    compile 'com.android.support:design:23.1.1'
}

and

// Top-level build file where you can add configuration options common to all sub-projects/modules.

buildscript {
    repositories {
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.0.1'

        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        jcenter()
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

I solved the problem myself. I upgraded the compileSdkVersion aswell as the minSdkVersion along with the dependencies. It now looks like this:

apply plugin: 'com.android.application'

android {
    compileSdkVersion 26
    buildToolsVersion

    defaultConfig {
        applicationId "com.example.Ron.myapp"
        minSdkVersion 18
        targetSdkVersion 26
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}


dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    testCompile 'junit:junit:4.12'
    compile 'com.android.support:appcompat-v7:26.0.2'
    compile 'com.android.support:design:26.0.2'
    compile 'com.android.support:cardview-v7:26.0.2'
}